JHM column East China Normal University Xie Bing team: Macrotranscriptome analysis reveals the mechanism of antibiotics affecting the co-digestion of kitchen waste and sludge to produce methane

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First author: Wang Panliang Corresponding author: Xie Bing Correspondence unit: School of Ecology and Environmental Science, East China Normal University Paper DOI: 10.
1016/j.
jhazmat.
2021.
127163 Picture Abstract Introduction Recently, East China Normal University Xie Bing The team of professors published a research paper titled "Metatranscriptomic insight into the effects of antibiotic exposure on performance during anaerobic co-digestion of food waste and sludge" in the Journal of Hazardous Materials, a well-known journal in the environmental field.
The effect of antibiotic exposure on the activities of functional microbial material metabolism and methanogenesis during the co-digestion of kitchen waste and sludge to produce methane, and the mechanism of microbial metabolism inhibiting the process of anaerobic digestion by antibiotic exposure was analyzed
.

A quick overview of the full text studies the effect of the addition of different types of antibiotics in the anaerobic co-digestion system of food waste and sludge on the process of anaerobic methane production
.

The results of the study showed that in addition to 5 mg/L erythromycin, tetracycline, sulfamethoxazole and erythromycin can inhibit and delay methane production
.

In contrast, tetracycline and sulfamethoxazole significantly inhibited cumulative methane production (p <0.
01)
.

The results of physical and chemical analysis showed that antibiotics inhibited the hydrolysis process and delayed the process of methanogenesis, which is consistent with the decrease in abundance of acetogens Proteiniphilum and Methanobacterium during anaerobic digestion
.

The results of the macrotranscriptome analysis showed that the main organic metabolism and energy metabolism activities of microorganisms were down-regulated under antibiotic exposure conditions, which resulted in the down-regulation of key coenzyme expression, which in turn inhibited the methane metabolism activity
.

In addition, the decrease in methane metabolism activity is completely consistent with the inhibition of the activity of the dominant methanogenic archaea Methanosarcina, confirming the contribution of Methanosarcina to methane production
.

This study provides new metatranscriptomic evidence for the effect of antibiotics on methane production during co-digestion
.

Introduction Anaerobic digestion is considered to be one of the most potential resource utilization technologies for organic solid waste
.

Under normal circumstances, in order to improve the efficiency of anaerobic treatment, the anaerobic co-digestion treatment strategy of kitchen waste and sludge is adopted in actual production
.

However, the residues of relatively high concentrations of antibiotics in sewage treatment systems, especially sludge, inevitably enter the anaerobic digestion system, and there is still a lack of research on the mechanism of antibiotics on the functional microorganisms and metabolic pathways in the digestion process
.

In this thesis, an anaerobic co-digestion reactor for food waste and sludge was constructed in the laboratory, and three different types of antibiotics were added to explore the effect of antibiotic exposure on anaerobic performance and the mechanism of action
.

The study focused on the anaerobic co-digestion process of food waste and sludge under antibiotic exposure conditions, and analyzed the changes in methane production and organic matter content during the hydrolysis and acidification process
.

Using high-throughput sequencing technology to analyze the microbial flora structure in the anaerobic digestion process, while using the macrotranscriptome method to study the changes in microbial activity and metabolic pathway expression during the process
.

The relevant results provide a scientific basis for a deeper understanding of the mechanism of the influence of antibiotic residues on the anaerobic digestion process
.

Graphic guide Figure 1: The effect of antibiotic exposure on methane production
.

In order to explore the effect of antibiotics on methane production during anaerobic digestion, the effects of exposure to different concentrations (5, 50 mg/L) of tetracycline, sulfamethoxazole and erythromycin on methane production were monitored
.

As shown in Figure 1, during the 70-day digestion process, the cumulative methane production of the control group (CK group and antibiotic-exposed group was between 482.
54 ± 11.
80 ~ 538.
98 ± 10.
42 ml CH4/g VS, and there was a significant difference between the groups (p <0.
01).
)
.

compared with the control, 50 mg / L sulfamethoxazole lowest cumulative production of methane (482.
54 ± 11.
80 ml of CH4 / G VS)
.

sulfamethoxazole, erythromycin and methane production inhibition rate of 5.
29 - 10.
16% , And as the concentration increases, its inhibitory effect increases
.

Figure 2: The effect of antibiotic exposure on (a) SCOD, (b) SPN and (c) SPS during anaerobic digestion
.

As shown in Figure 2, in the 23rd day (maximum daily methane production phase), the concentration of CK group SCOD (7040 ± 405.
10 mg / L ) and SPN (217.
59 ± 1.
26 mg / L ) were lower than antibiotic exposure group (P <0.
05)
.

this is illustrated in the antibiotic Under pressure, the utilization rate of organic matter by microorganisms decreases and the hydrolysis activity of microorganisms is inhibited
.

Figure 3: The effect of antibiotic exposure on volatile fatty acids (VFAs) during anaerobic digestion
.

The production of VFAs is the main feature of anaerobic digestion and acidification.

.

3, the total concentration of the starting phase VFAs was 85.
25 ± 7.
27 mg / L, on day 10, the total concentrations of VFAs rose rapidly to group (3957.
09 ± 224.
17) ~ (4612.
17 ± 278.
36) mg / L
.

With the progress of anaerobic digestion, the total concentration of VFAs continues to decrease
.

Compared with the concentration levels of propionic acid, butyric acid, isovaleric acid and n-valeric acid, acetic acid is the main type of VFAs because acetic acid is the key VFAs in the anaerobic digestion process because it is directly related to methane production
.

On the 23rd day (the maximum daily methane production period), the acetic acid content in the CK group was the lowest (1951.
20 ± 16.
97 mg/L), indicating that antibiotics reduced the utilization efficiency of acetic acid, thereby inhibiting the acidification process
.

Figure 4: The effect of antibiotic exposure on dominant bacteria (a) and archaea (b) during anaerobic digestion
.

Figure 4a shows the change of bacterial flora under antibiotic exposure
.

Compared with the initial stage, the proteolytic bacteria Fastidiosipila declined during the peak period of methanogenesis (day 23), and then increased at the end of the methanogenesis period
.

Fastidiosipila can convert carbohydrates and proteins into VFAs
.

During the peak period of methanogenesis, antibiotic exposure reduced the abundance of Proteiniphilum
.

Proteiniphilum can accelerate the conversion of organic acids to acetic acid through the metabolic pathway of acetic acid production
.
The decrease in its abundance indicates that the antibiotic inhibits the acetic acid production process .

It can be seen from Figure 4b that Methanosaeta (37.
66 ± 19.
94%) and Methanosarcina (46.
27 ± 18.
02%) are the main methanogens during the peak period of methanogenesis
.

Methanosarcina can participate in various methane production pathways and play a key role in methane production
.

Compared with the CK group, the Methanosaeta abundances in the tetracycline and erythromycin supplementation groups were reduced
.

In addition, the abundance of hydrogenotrophic methanogens in all antibiotic-added groups decreased, indicating that the hydrogen production process under antibiotic pressure was inhibited, thereby inhibiting the methanogenesis process
.

Figure 5: Metatranscriptomics analysis reveals changes in microbial metabolic pathways and community expression under antibiotic exposure
.

As shown in Figure 5a, under the exposure of antibiotics, methane metabolism was inhibited, confirming that antibiotics inhibited the functional activity of methane metabolism
.

In contrast, tetracycline and sulfamethoxazole have the strongest inhibitory effects, with inhibitory rates of 71.
73% and 32.
64%, respectively
.

In addition, tetracycline and sulfamethoxazole reduced the abundance of mRNA related to major organic metabolism (such as amino acid metabolism, lipid metabolism) and energy metabolism, while erythromycin down-regulated the expression of energy metabolism (Figure 5b)
.

These results indicate that the metabolism of organic matter is relatively inactive when exposed to tetracycline and sulfamethoxazole
.

VFAs can be produced through lipid metabolism.
The inhibition of lipid metabolism expression indicates that tetracycline and sulfamethoxazole inhibit the production of VFAs
.

As shown in Figure 5c
.

Process methanogenic main methanogens is Methanosarcina, Methanobacterium the like
.

The expression of Methanosarcina was somewhat suppressed in the antibiotic exposure group
.

In addition to erythromycin, other antibiotics also inhibit the activity of Methanobacterium and Methanoculleus
.

Tetracycline and sulfamethoxazole also inhibited the activity of Geobacter involved in the direct interspecies electron transfer pathway (Figure 5d), thereby reducing the electron transfer efficiency and inhibiting methane production to a certain extent
.

Figure 6: Expression (a) and changes in abundance (b) of methane metabolic pathways under antibiotic exposure
.

Figure 6 analyzes the four metabolic pathways of methanogenesis (M00357, M00356, M00563, and M00567)
.

It is worth noting that, compared with the control, antibiotics significantly inhibited these pathways, while the inhibition of erythromycin was lower (Figure 6b), indicating that antibiotic exposure inhibited the key step of methane production
.

Among the four methanogenesis pathways, acetic acid nutrient-type methanogenesis has the highest metabolic activity, indicating that methane production in the co-digestion process of food waste and sludge is mainly produced through the acetic acid-type nutrient-type methanogenesis metabolic pathway, which is in line with the change trend of dominant bacteria Methanosarcina Consistent (Figure 5c)
.

At the same time, the acetate-trophic methanogenesis metabolic pathway (M00357) was inhibited by 73.
41% and 7.
51% under tetracycline and sulfamethoxazole exposure, respectively (Figure 6b)
.

To further clarify the inhibitory effect of antibiotic exposure on methane metabolism, we analyzed the biosynthetic activity of key coenzymes (Coenzyme M, Coenzyme B, Coenzyme F420 and Methanefuran) for methanogenesis
.

The results showed that both tetracycline and erythromycin reduced the synthesis activity of related coenzymes, while sulfamethoxazole inhibited the synthesis activity of coenzyme M, coenzyme F420 and methanefuran, thereby affecting the metabolic activity of methane
.

Summary This study used the macrotranscriptome technology to clarify the microbiological mechanism of antibiotics inhibiting the co-digestion process of food and sludge
.

In the process of anaerobic digestion, antibiotic exposure inhibits the expression of key organic matter metabolism (amino acid metabolism, lipid metabolism) and the expression of mRNA related to energy metabolism, resulting in biological production of key coenzymes (Coenzyme B/M/F420 and methanefuran).
The synthesis activity is inhibited, and finally the metabolic activity of methanogenesis is inhibited
.

These results are consistent with material metabolism and methane production
.

The research results expand the understanding of antibiotics inhibiting methane production from organic solid waste
.

This research was funded by the National Key Research and Development Program (2018YFC1901000), the National Natural Science Foundation of China (21577038) and the Shanghai Science and Technology Commission (20232420700)
.

About the author Corresponding author: Xie Bing, PhD, professor and doctoral supervisor of the School of Ecology and Environmental Sciences, East China Normal University
.

The research direction is sewage, organic solid waste and soil pollution control and resource utilization, the migration and transformation mechanism of emerging pollutants, and strengthened control
.

Presided over more than 30 projects including the key research and development solid waste special projects of the Ministry of Science and Technology, the National Natural Science Foundation of China, and provincial and ministerial key projects
.

A total of more than 180 domestic and foreign academic papers have been published, including more than 90 SCI papers, many of which are highly cited by ESI; 4 monographs have been published; more than 10 national invention patents have been transferred
.

Take the lead in obtaining a number of provincial and ministerial awards
.

Contact email: bxie@des.
ecnu.
edu.
cn First author: Wang Panliang, male, PhD student, currently studying in the School of Ecology and Environmental Science, East China Normal University, his main research direction is emerging pollution behavior and control in the environment
.

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.

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.

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